Silicon-on-insulator (SOI) metal oxide semiconductor field effect transistors (MOSFETs) are well known in the field of semiconductors. SOI MOSFETs have been demonstrated to be superior to bulk silicon MOSFETs in low-power, high-speed very large scale integration (VLSI) applications. The advantages include 1) less junction capacitance so that higher circuit speed can be achieved; 2) better device isolation; and 3) sufficient radiation hardness.
FIG. 1 depicts a SOI MOSFET semiconductor structure 100 of the prior art. Structure 100 includes insulator 114 positioned over bottom substrate layer 116. Insulator 114 surrounds body region 112. Source region 108 and drain region 110 are positioned within body region 112, and gate electrode 106 is positioned above body region 112. Side wall spacers 122 and 124 surround gate electrode 106. A barrier layer 118 and oxide layer 120 are formed over insulator 114, source region 108, drain region 110, and gate electrode 106. Electrical contacts 102 and 104, source region 108, and drain region 110 are formed through barrier layer 118 and oxide layer 120.
As shown, electrical contacts 102 and 104 only contact respective source region 108 and drain region 110. Body region 112 is electrically isolated and therefore its voltage varies with the voltages applied to either source region 108, drain region 110, or gate electrode 106. When a voltage applied to a source or drain region changes, the voltage of body region 112 also changes to accommodate the change in applied voltage, but in a different amount of time than it takes the source or drain terminals to achieve the applied voltage. The voltage of body region 112 varies undesirably because the body region is electrically isolated (so called "floating body effect"). The floating body effect introduces undesirable effects.
Floating body effects cause, for example, sharp increases in the relationship between drain current and drain voltage (so called "kink effect"), anomalous subthreshold current, transient current overshoot, and early device voltage V.sub.DS breakdown. The kink effect may lead to lower device gain, which is undesirable in analog applications. Floating body effects remains a major obstacle to acceptable operation of SOI MOSFET transistors.
What is needed is an SOI MOSFET semiconductor structure and method of fabricating the SOI MOSFET semiconductor structure which controls the floating body effects.